A lot of power sources are distributed in our environment, such as sunlight, surf, wind. It is an important problem how to collect these energies. Power networks are thus used to resolve this problem.
In a series DC power network of the prior art, when more and more DC power cells are connected to the network, the currents in the network approach to constant values and the power collected by the target load through the network thus approaches a constant. In the same time, the output powers of the DC power cells in the series DC power network of the prior art approach zero. The same problem occurs in a parallel DC power network of the prior art. Series and parallel DC power networks of the prior arts are not suitable for collecting the power of distributed DC power cells. A series-parallel DC power network of the prior art does not induce the above problem when more and more DC power cells are connected to the network, however, it will generate a non-uniform power distribution among the DC power cells thereof. The non-uniform power distribution causes some DC power cells to be inversely charged. In order to prevent the damage of inversely charging DC power cells, diodes are connected in series or parallel to DC power cells. Although the above problems are resolved by using the series-parallel DC power network with diodes, the power efficiency of the network is low when the electric powers of large amount of DC power cells are collected.